Fix dbg() under node to go to stderr (#24406)

This was accidentally changed to stdout in #23999.  Oops.

Fixed: #24403

Author: sbc100

src/runtime_debug.js

@@ -18,7 +18,7 @@ function dbg(...args) {
     var fs = require('fs');
     var utils = require('util');
     var stringify = (a) => typeof a == 'object' ? utils.inspect(a) : a;
-    fs.writeSync(1, args.map(stringify).join(' ') + '\n');
+    fs.writeSync(2, args.map(stringify).join(' ') + '\n');
   } else
 #endif
   // TODO(sbc): Make this configurable somehow.  Its not always convenient for

test/test_other.py

@@ -15029,7 +15029,11 @@ def test_dbg(self):
     self.emcc_args.append('--pre-js=pre.js')
     # Verify that, after initialization, dbg() messages are prefixed with
     # worker and thread ID.
-    self.do_runf('other/test_dbg.c', expected, regex=True)
+    self.do_runf('other/test_dbg.c', expected, interleaved_output=True, regex=True)
+
+    # Verify that stdout does not contain dbg() messages (interleaved_output=True
+    # means we return stdout followed by stderr)
+    self.do_runf('other/test_dbg.c', 'hello, world!\nstart { foo: 1 }\n', interleaved_output=False)
 
     # When assertions are disabled `dbg` function is not defined
     self.do_runf('other/test_dbg.c',